The leading cause of premature tire failure is improperly fitted tires. Underinflated or overinflated tires can result in vehicle damage, inadequate traction, low gas mileage, premature tread wear, and blowouts, i.e., spontaneous destruction of the tire.
Presently known devices for determining tire pressure are unsatisfactory in several regards. For example, existing techniques for measuring tire pressure typically involve coupling a mechanical pressure sensor to the valve stem and reading a lineal gauge extending from the sensor. See, for example, Guy U.S. Pat. No. 3,592,218, issued July 13, 1971. This procedure is time consuming, cumbersome, and wholly unsuited for use in inclement weather, especially when the vehicle may have up to eighteen or more wheels.
Tire pressure sensors configured to be mounted directly to the tire valve stem are also known. See, for example, Winther U.S. Pat. No. 3,827,393, issued Aug. 6, 1974. The Winther device comprises a pressure differential sensor disposed within a cylindrical housing, which housing is threadedly attached to the valve stem. When the tire is properly inflated, the pressure at the differential pressure sensor valve is sufficient to overcome a spring force which acts on the valve seat. When the pressure within the tire drops below a predetermined threshold, the differential pressure sensor valve moves in the spring biased direction, porting tire pressure to a slideable piston assembly having a visibly conspicuous piston rod disposed to project axially from the valve assembly at low tire pressures.
Another known device involves a cap designed to replace existing standard valve stem caps. The color exhibited by the cap changes with a decrease in tire pressure, thus providing visual indicia of tire pressure loss.
Yet another known tire pressure sensing device produces a digital LCD readout indicative of tire pressure when the hand-held sensor is brought into engagement with the valve stem. Such a device is available from Leichtuug Workshops of Cleveland, Ohio, catalog No. 93153.
The foregoing devices are unsatisfactory in several regards. For example, in many of the devices, the operator must remove the valve stem cap, engage the pressure sensor with the valve stem, observe a reading, and thereafter replace the valve stem cap. This procedure must then be repeated for each tire. Other of the foregoing devices are designed to replace the existing valve stem cap, so that the pressure sensing device need only be removed when it is necessary to inflate the tire. These latter devices, however, do not indicate the magnitude of the pressure level in the tire; rather, they merely indicate whether the pressure is above or below a predetermined threshold. Further, many prior art devices rely on visual indicia at or physical connections to the tire stem, which is often neither readily visible nor accessible, e.g., the interior tires of coaxial sets of tires on 18 wheel trucks.
A tire pressure sensing device is needed which overcomes the shortcomings of the prior art.